Vibrissae (whiskers) are important components of the mammalian tactile sensory system, and primarily function as detectors of environmental vibrotactile cues. Pinnipeds possess the largest and most highly innervated vibrissae among mammals and their vibrissae demonstrate a diversity of shapes and likely mechanical properties. These two characteristics are important for vibrotactile sensory perception. Vibrissae of most phocid seals exhibit a beaded morphology with repeated sequences of crests and troughs along their length. I comparatively characterized differences in vibrissae morphologies among phocid species with a beaded profile, phocid species with a smooth profile, and otariids with a smooth profile using traditional and geometric morphometric methods to test the hypothesis that vibrissal morphologies are species-specific manipulations of a common pattern. The traditional and geometric morphometric datasets were subsequently combined by mathematically scaling each to true rank, followed by a single eigendecomposition. Quadratic discriminant function analysis demonstrated that 79.3, 97.8 and 100% of individuals could be correctly classified to taxon based on vibrissal shape variables in the traditional, geometric and combined morphometric analyses, respectively. At least three separate morphologies were identified since phocids with beaded vibrissae, phocids with smooth vibrissae, and otariids each occupied distinct morphospace in the geometric morphometric and combined data analyses. Another important characteristic that influences the transduction of vibrotactile information to the mechanoreceptors in the follicle-sinus complex is the materials properties of the vibrissae. Vibrissae were modeled as cantilever beams and flexural stiffness (EI) was measured to test the hypotheses that the shape of beaded vibrissae reduces flexural stiffness and that vibrissae are anisotropic (orientations differ in EI). Species were significantly different and smooth vibrissae were generally stiffer than beaded vibrissae. Beaded vibrissae decrease vibrations in flow, which, combined with lower flexural stiffness values, may enhance detection of small changes in flow from swimming prey. The anterior plane of the vibrissae is likely the most biologically significant in tracking hydrodynamic trails but had lower flexural stiffness values than the dorsoventral orientation. There is likely a complex interaction between shape and mechanical properties in pinniped vibrissae but the ecological and functional implications are currently unknown.

Electroplated zinc finishes have been widely used in the packaging of electronic products for many years as a result of their excellent corrosion resistance and relatively low cost. However, the spontaneous formation of whiskers on zinc electroplated components, which are capable of resulting in electrical shorting or other damaging effects, can be highly problematic for the reliability of long life electrical and electronic equipment. To date, most research has focused on tin whiskers and much less attention has been paid to zinc whisker research. A number of mechanisms to explain zinc whisker growth have been proposed, but none of them are widely accepted and some are in conflict with each other. This study has investigated the mechanism for whisker growth from three commercial zinc electroplated coatings on mild steel substrates. Firstly, whisker growth from an alkaline cyanide-free zinc electrodeposit was studied. A reduction in deposition current density (from 50 to 5 mA/cm2) and an increase in deposit thickness (from 2 to 15 μm) both contributed to reduced whisker growth. In terms of the mechanisms of whisker growth, it was observed that the presence of spherical raised surface features (nodules) with cavities beneath, promoted whisker growth by markedly shortening the incubation time from ~ 5 months to ~ 4 weeks. More importantly, the time dependent recrystallisation of the as-deposited columnar structure is closely associated with whisker growth from both nodules and planar regions of the deposit. The formation of Fe-Zn intermetallic compounds (IMCs) was not observed at either the Fe/Zn interface or within the electroplated coatings and does not appear to be associated with Zn whisker growth. Whisker growth from an acid chloride zinc electroplated coating and a Zn-Ni alloy electroplated coating were also investigated. These two coatings were immune to whisker growth after 18 months of storage at room temperature, regardless of deposition current density, deposit thickness and substrate surface modification. Finally, the effect of potential mitigation strategies on whisker growth was evaluated. Exposure to elevated temperatures (50 to 150°C) for 24 hours promoted whisker growth by reducing the incubation time for whiskers to first appear from less than 4 weeks to less than 10 days, whilst whisker growth was significantly retarded when samples were subjected to a short period of thermal treatment (50 to 150°C) for 0.5 hour. More importantly, for a short period of thermal treatment, whisker mitigation became increasingly effective as the treatment temperature was raised. In addition, the formation of a trivalent chromium passive coating on the alkaline cyanide-free zinc electrodeposits immediately after deposition was not an effective mitigation method to retard whisker growth.

Les batteries Li-ion sont la technologie de référence pour l'électronique portable, et l'un des objectifs est le développement de cette technologie pour des applications demandant de fortes densités d'énergie, comme la traction. Ce travail, mené dans le cadre du projet Européen AMELIE- Green Car, porte sur deux aspects. Le premier concerne la synthèse et la caractérisation de nouveaux solvants et sels performants et pouvant être utilisés avec des matériaux à haut potentiel tels que LiNi1/3Mn1/3Co1/3O2 ou LiNi0,4Mn1,6O4, en remplacement des électrolytes courants à base de LiPF6 et de carbonates, qui induisent une forte d'autodécharge et présentent des stabilités thermique et chimique insuffisantes. L'utilisation de carbonates, carbamates et sulfonamides fluorés en tant que solvants, permet d'obtenir, pour certaines des formulations évaluées, des performances comparables aux références commerciales, malgré des conductivités inférieures. De plus, la fluoration confère à ces molécules des stabilités thermique et électrochimique améliorées. En ce qui concerne les sels, plusieurs nouvelles structures ont été synthétisées et testées en combinaison avec des solvants commerciaux, avec des résultats intéressants du point de vue de la conductivité et du comportement électrochimique.La deuxième partie de ce travail concerne la mise en forme, par des procédés industriels, de séparateurs minces à base de polymères fluorés, qui présentent des performances comparables aux séparateurs commerciaux. Des membranes denses et poreuses ont été élaborées à partir de plusieurs grades de PVDF. Les membranes poreuses élaborées, présentant des taux de porosité élevés, montrent de faibles tenues mécaniques, deux stratégies de renfort ont ainsi été étudiées : la première via la réticulation des membranes après greffage de groupements polymérisables, la deuxième via l'incorporation de Cellulose Nano Cristalline (CNC), formant un réseau percolant permettant le renfort. Les deux méthodes ont donné des résultats prometteurs sur les membranes denses : le module de conservation augmente entre 2 et 5 fois à 25°C tout en conservant des performances électrochimiques intéressantes. Le transfert de ces propriétés aux membranes poreuses est encore à optimiser ; cependant un renfort partiel a été obtenu pour les membranes composites poreuses, ce qui en fait, en combinaison avec une bonne conductivité (largement au dessus de 1mS/cm) et porosité, des candidats attractifs pour des accumulateurs Li-ion à charge rapide. / Li-ion batteries have become the dominant power storage devices for portable electronics, and researchers are still at work to broaden their field of use to high energy density devices, like cars. Within the framework of the collaborative project AMELIE - Green car, this study articulates along 2 main axes. The first one deals with the synthesis and characterization of new fluorinated solvents and salts to replace, for the use with high potential materials such as LiNi1/3Mn1/3Co1/3O2 or LiNi0,4Mn1,6O4, the commonly used LiPF6 and carbonate-based electrolytes, which suffer from a high self-discharge ratio, and an insufficient thermal and chemical stability. The use of fluorinated carbonates, carbamates, and sulfonamides as solvents provides performances as good as the commercial references, even if we register a visible loss in conductivity. Moreover, the fluorination provides these molecules with higher thermal and electrochemical stabilities. About the salts, several new structures of sulfonamide salts were synthesized and tested in combination with commercial solvents, with interesting results from the point of view of conductivity and the electrochemical stability.The second part of this study deals with the development of thin perfluorinated separators, which could compete with commercial references such as Celgard® separators and whose production could be easily up-scale. To do this, dense and porous separators were prepared from several PVdF grades. Since the porous membranes, the most promising for the battery applications, suffer from a relatively low mechanical strength, 2 reinforcement techniques were also evaluated: the first one consists in cross-linking the polymer after grafting of polymerizable groups; the second one consists in adding Nano Cristalline Cellulose (NCC) particles to form a reinforcing percolating network. Both methods give promising results with dense membranes: a 2- to 5-fold increase of storage modulus is observed at 25°C, in addition to interesting electrochemical properties. The transfer of these promising results to the porous membranes is still to be optimized, but a partial reinforcement was obtained for nano-composites porous membranes, while the good conductivity (still largely superior to 1 mS/cm) and porosity make them attractive options for high charge rate batteries.

Les whiskers, filaments métalliques qui poussent sur des surfaces métalliques, sont unproblème très important pour la fiabilité des composants électroniques. Depuis ces dernièresannées, il y a eu un regain d’intérêts industriels dans le domaine de la croissance des whiskers,principalement en raison de la miniaturisation des dispositifs électroniques et des réglementationsenvironnementales interdisant l'utilisation du plomb.Alors que la plupart des recherches concernent les whiskers d'étain, il y a encore peu detravaux sur les whiskers de zinc. Les revêtements d’électrodéposés de zinc sont utilisés commeprotection anticorrosion pour les aciers faiblement alliés dans diverses industries, commel'automobile, l'aéronautique ou l'énergie, ainsi que dans les structures de soutien ou les planchersfaux plafonds dans les centres de données informatiques. Afin d'atténuer, de prévenir et deprédire les défaillances causées par les whiskers de zinc, les mécanismes de sa croissance doiventêtre compris.Grâce à des tests de stockage accéléré et à des observations par microscopie électronique àbalayage (MEB), la cinétique de croissance des whiskers de zinc a été étudiée sur des tôles d'acierau carbone faiblement allié, galvanisé et chromé. Afin de comprendre les mécanismes de lacroissance des whiskers de zinc, la caractérisation quantitative ainsi que les excroissances (densité,volume et vitesse de croissance) ont été reliées aux paramètres suivants: la température, le bainpour l’électrodéposition du zinc, la chromatation, l’épaisseur du substrat d’acier, l’épaisseur durevêtement de zinc ainsi que la contrainte résiduelle.En outre, la microstructure et la cristallographie du revêtement de zinc, des racines deswhiskers ainsi que des whiskers elles-mêmes ont été étudiées par diffraction des électronsrétrodiffusés (EBSD), microscopie électronique à transmission (MET), microanalyse par rayon X(EDX) et le dispositif ASTAR pour l'orientation locale des grains; la préparation des échantillonsa été réalisée à l’aide d’un faisceau d'ions focalisés (FIB). La recristallisation ainsi que lesdislocations dans les whiskers et les excroissances ont été observés; aucun composéintermétallique n’a été observé que ce soit dans les échantillons issus de différents bainsélectrolytes ou encore dans les films / whiskers.Il a été montré que la relaxation de contrainte de compression résiduelle et la croissance deswhiskers sont deux phénomènes différents mais fortement reliés et thermiquement activés.Chacun d'entre eux suit un mécanisme différent; les énergies d'activation apparentes des deuxphénomènes ont été établies, et la diffusion aux joints de grains est proposée comme le principalmécanisme de diffusion pour la croissance des whiskers.Des cinétiques de la croissance des whiskers, à la fois analytique et phénoménologique sontproposées. Une bonne estimation de la croissance des whiskers et de leur vitesse de croissance àdes températures proches des conditions de fonctionnement est obtenue par comparaison avecles données expérimentales. / Whiskers, conductive metallic filaments that grow from metallic surfaces, are a very importantissue for reliability of electronic components. Through recent years, there has been a renewedindustrial interest on whisker growth, mainly due to the miniaturization of electronic devices andthe environmental regulations forbidding the use of lead.While most of the research has been focused on tin whiskers, there is still little reference tozinc whiskers. Electroplated zinc coatings are actually used as anticorrosive protection for lowalloy steels in diverse industries such as automotive, aerospace or energy, as well as for supportstructures or raised-floor tiles in computer data centers. In order to mitigate, prevent and predictthe failures caused by the zinc whiskers, the mechanisms of growth must be understood.By accelerated storage tests and Scanning Electron Microscopy (SEM) observation, kinetics ofgrowth of zinc whiskers was studied on low alloy chromed electroplated carbon steel.Quantitative characterization of both whisker and hillocks (density, volume and growth rate) wasrelated with the parameters temperature, electroplating electrolyte, presence of chrome, steelsubstrate thickness, zinc coating thickness and residual stress, in order to understand themechanisms of growth.Additionally, both microstructure and crystallography of zinc coating, whisker roots and actualwhiskers were studied by Electron Backscatter Diffraction (EBSD), Transmission ElectronMicroscopy (TEM), Energy-dispersive X-ray spectroscopy (EDX) and local grain orientationwith ASTAR setup, using Focused Ion Beam (FIB) for samples preparation. Recrystallization aswell as dislocations were observed in both whiskers and hillocks; no intermetallic compoundswere seen in neither electroplated nor whiskers.It is found that compressive residual stress relaxation and whiskers growth are two differentbut strongly interconnected phenomena both thermally activated, an each of them follows adifferent mechanism; apparent activation energies of the two phenomena are calculated, andgrain boundary diffusion is established as the main diffusion mechanism for whiskers growth.Whiskers growth kinetics, both analytical and phenomenological is proposed. Goodestimation of whiskers growth and whiskers growth rate at temperatures close to operationconditions is obtained when compared with experimental data. / Whiskers, filamentos metálicos que crecen en superficies metálicas, son un problema muyimportante para la fiabilidad de componentes electrónicos. Durante los últimos años, ha habidoun renovado interés industrial en el crecimiento de whiskers, debido principalmente a laminiaturización de dispositivos electrónicos y a las regulaciones ambientales que prohíben lautilización de plomo.La mayoría de las investigaciones se concentran en los whiskers de estaño y hay todavía pocostrabajos sobre los whiskers de zinc. Los recubrimientos de zinc electrodepositado son utilizadoscomo protección anticorrosión para los aceros de baja aleación en diversas industrias, comoautomotriz, aeronáutica o energética, así como en la estructuras de soporte o tejas de techosfalsos en los centros de datos informáticos. Para atenuar, prevenir y predecir las fallas causadaspor los whiskers de zinc, los mecanismos de crecimiento deben ser comprendidos.Gracias a experimentos de almacenamiento de muestras y a observaciones por microscopíaelectrónica de barrido (SEM), la cinética de crecimiento de whiskers de zinc ha sido estudiada enaceros de baja aleación recubiertos de zinc y cromados. Para comprender los mecanismos decrecimiento de whiskers de zinc, la caracterización cuantitativa de whiskers y de protuberancias(densidad, volumen y velocidad de crecimiento) fue relacionada con los parámetros siguientes:temperatura, electrolito usado en la electrodeposición de zinc, cromado, espesor del substrato deacero, espesor del recubrimiento de zinc al igual que el estrés residual.Adicionalmente, microestructura y cristalografía del recubrimiento de zinc, de raíces dewhiskers así como de los propios whiskers fueron estudiadas por medio de la difracción deelectrones por retrodispersión (EBSD), microscopía electrónica de transmisión (TEM),microanálisis por rayos X (EDX) y el dispositivo ASTAR para la orientación local de granos; lapreparación de muestras fue realizada con la ayuda de un haz de iones localizados (FIB). Larecristalización así como las dislocaciones en whiskers y protuberancias fueron observadas;ningún compuesto intermetálico ha sido observado en los recubrimientos ni en los whiskers.Se determinó que la relajación del estrés residual de compresión y el crecimiento de whiskersson dos fenómenos diferentes pero fuertemente interconectados y térmicamente activados. Cadauno de ellos sigue un mecanismo diferente; las energías de activación aparentes de los dosfenómenos han sido establecidas, y la difusión por bordes de grano es propuesta como elprincipal mecanismo de difusión para el crecimiento de whiskers.Cinéticas de crecimiento de whiskers, a la vez analíticas y fenomenológicas son propuestas.Una buena estimación del crecimiento de whiskers y su velocidad de crecimiento a temperaturascercanas a las condiciones de operación es obtenida por comparación con los datosexperimentales.

Made available in DSpace on 2016-06-02T19:19:56Z (GMT). No. of bitstreams: 1 CESAR_Natalia_2013.pdf: 4350279 bytes, checksum: 6bb996ac8fb178b63b5845f8f96653d3 (MD5) Previous issue date: 2013-02-19 / Financiadora de Estudos e Projetos / Composite is a material composed mainly of two phases, the matrix which is continuous and surrounds the other phase, which is called the dispersed phase or stage reinforcement. Nanocomposites are obtained by incorporating reinforcing agent in nanosize in matrices of various origins. The properties of these materials depend on the whiskers, the polymer matrix and the interaction at the interface. Interest in cellulose nanocrystals has grown due to exceptional mechanical characteristics of these materials, the environmental benefits and the low cost. The greatest difficulty in producing them is due to the lack of compatibility with polymer matrices, because the matrices typically exhibit hydrophobic character as opposed to the hydrophilic character of the whiskers, with low interaction in the region of the interface material properties are negatively affected . Among the existing polymer matrix is cellulose acetate polymer which is a cellulose derivative. For the use of whiskers in a matrix of ethyl cellulose, a change in the nanocrystal surface of cellulose using Dianidrido benzofenona tetracarboxílico ou 3,3 ,4,4 (BTDA) was performed. The main objective of this work was to prepare and characterize nanocomposites consisting of cellulose acetate reinforced with whiskers (with and without chemical modification of the surface). It was possible to characterize chemical, thermal and morphologically fibers (young and senescent) of crude and bleached macrophyte Typha domingensis, like whiskers that were extracted from the central parts (young and senescent) of this macrophyte, and it was also possible to characterize acetate films cellulose (mother) and nanocomposites reinforced with whiskers (with and without surface modification). Of all the films prepared, this project allowed select the best property that had mechanics that the nanocomposite was 1.1% - whiskers (senescent) with surface modification and ultrasound, its tensile strength showed an improvement of 66.26% compared to cellulose acetate film. / Compósito é um material constituído basicamente por duas fases; a matriz a que é contínua e envolve a outra fase, que é denominada fase dispersa ou fase reforço. Nanocompósitos são obtidos pela incorporação de agente de reforço de tamanho nanométrico em matrizes de diversas origens. As propriedades destes materiais dependem dos whiskers, da matriz polimérica e da interação na interface. O interesse por nanocristais de celulose tem crescido devido às características mecânicas excepcionais destes materiais, dos benefícios ambientais e do baixo custo. A maior dificuldade em produzi-los é decorrente da falta de compatibilidade com as matrizes poliméricas; pois as matrizes, geralmente, apresentam caráter hidrofóbico em oposição ao caráter hidrofílico dos whiskers; com a baixa interação na região da interface as propriedades do material são afetadas negativamente. Dentre as matrizes poliméricas existentes encontra-se o acetato de celulose que é um polímero derivado da celulose. Para a utilização dos whiskers em matriz de acetato de celulose, uma mudança superficial nos nanocristais de celulose utilizando Dianidrido benzofenona tetracarboxílico ou 3,3 ,4,4 (BTDA) foi realizada.O objetivo principal deste trabalho foi preparar e caracterizar nanocompósitos constituídos de acetato de celulose reforçados com whiskers (com e sem modificação química de superfície). Foi possível caracterizar química, térmica e morfologicamente as fibras (jovem e senescente) brutas e branqueadas da macrófita Typha domingensis, assim como os whiskers que foram extraídos das partes centrais (jovem e senescente) desta macrófita, e também foi possível caracterizar os filmes de acetato de celulose (matriz) e os nanocompósitos reforçados com os whiskers (com e sem modificação química de superfície). Dentre todos os filmes preparados, este projeto permitiu selecionar o que apresentou melhor propriedade mecância que foi o nanocompósito 1,1% - whiskers (senescente) com modificação superficial e ultrasom, sua resistência a tração apresentou uma melhoria de 66,26% se comparado ao filme de acetato de celulose.

Made available in DSpace on 2015-04-01T12:17:40Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 2177616 bytes, checksum: bad1b5abac746f9000b37ffd93fc28e9 (MD5) Previous issue date: 2013-09-17 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Natural fibers were studied to investigate possibilities and better treatment techniques for the development of nanocomposites with poly(glycerol sebacate) (PGS). In this study, the potential of plants such as caroá (Neoglaziovia variegata) and macambira (Bromelia laciniosa) was investigated as sources of natural fibers to obtain whiskers by acid hydrolysis. Fibers were obtained from plant leaves of each species were pre-treated with alcohol and water to remove impurities, treated with aqueous sodium hydroxide (mercerization) and then with sodium chlorite (bleaching) before hydrolyzing with sulfuric acid in order to obtain cellulose whiskers. Fibers and whiskers were characterized thermogravimetric analysis (TGA), X-ray diffraction (XRD) and the morphology was analyzed by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). Polymers and composites reinforced with whiskers were characterized by TGA, DSC, mechanical (tensile) tests and Fourier Transform Infrared Spectroscopy (FTIR). Results show that it was possible to extract whiskers from both natural and macambira and composite properties were dependent on whisker content. / O objetivo desta pesquisa foi estudar técnicas de obtenção e tratamento de fibras naturais para o desenvolvimento de nanocompósitos com o poli(glicerol sebacato). Nesse trabalho foram investigadas as potencialidades das plantas caroá (Neoglaziovia variegata) e macambira (Bromelia laciniosa) como fontes de fibras naturais para obtenção de whiskers a partir de hidrólise ácida. As fibras foram obtidas das folhas de ambas, separadas por processamento manual, pré tratadas com água e álcool (lavagens) para retirada de impurezas, tratadas com soluções aquosas de hidróxido de sódio (mercerização) e em seguida tratadas com clorito de sódio (branqueamento), onde se obteve uma massa com alto teor de celulose e então foi tratada com ácido sulfúrico em procedimento de isolamento para a obtenção de whiskers de celulose. As fibras foram caracterizadas por análise química, análise termogravimétrica (TGA), a cristalinidade foi investigada por difratometria de raios-X (DRX) e a morfologia foi investigada através de microscopia eletrônica de varredura (MEV). Os whiskers obtidos das fibras foram caracterizados por microscopia de força atômica (AFM), por TGA e por DRX. As reações de síntese do poli(glicerol sebacato) (PGS) se deram em temperaturas relativamente baixas (120ºC), através da policondensação e em atmosfera inerte de argônio ou nitrogênio, sem o uso de catalisadores externos. Os polímeros e compósitos reforçados com whiskers foram caracterizados por TGA, calorimetria exploratória diferencial (DSC), caracterização mecânica em ensaios de tração e por espectroscopia na região do infravermelho por transformada de Fourier (FTIR). As superfícies fraturadas nos ensaios de tração foram observadas por MEV. Os nanocompósitos apresentaram uma grande variação nas propriedades mecânicas com os teores de fibras, indicando a influência dos whiskers na matriz, aumentando o módulo e a resistência e diminuindo a elasticidade.

Thesis (MTech (Nature Conservation))--Cape Peninsula University of Technology, 2017. / Stable isotope analysis (SIA) of whiskers has been used to identify temporal feeding habits, intra-population diet variation, as well as individual dietary specialisation of marine and terrestrial carnivores. However, the potential of the method to disclose such dietary information for large wild felids has been little explored. The accurate interpretation of stable isotope ratios along serially sampled whiskers is hampered by lack of information on species-specific whisker growth rates, whisker growth patterns and whisker-diet trophic discrimination factors (TDFs). Whisker growth rate and growth pattern informs on the time period encapsulated in the analysed segment of a whisker, while whisker-diet TDFs are required to make correct deductions of the prey species consumed by a predator. The aim of this study was to develop and evaluate the technique of using stable carbon and nitrogen isotope analysis of felid whiskers to quantify the diet of wild felids and in particular, to identify diet variation among individuals. To achieve this, lion Panthera leo and leopard Panthera pardus whisker growth rate and growth pattern, and lion whisker-diet TDFs were measured, using captive individuals held at the National Zoological Gardens, Pretoria. The viability and applicability of the technique was then explored on six free-ranging leopards in Phinda Private Game Reserve (hereafter Phinda), northern KwaZulu-Natal (KZN) whose diets have been intensively studied using traditional methods. Whisker growth rates and growth patterns were measured for four lions (three sub-adult females and one adult male) and an adult male leopard over 185 days using giraffe Giraffa camelopardalis meat as an endogenous biomarker to consecutively mark whiskers as they grew. The 13C-depleted, C3-derived giraffe meat with its characteristic isotopic signature could be discerned from the 13C-enriched diet of C4 grain-fed beef and chicken the felids were sustained on. Two whiskers were removed from each felid at the beginning of the experiment, and felids were fed the giraffe meat at four predetermined periods to mark the whiskers replacing the removed ones. The periods with low δ13C values, identified following serial sectioning of the regrown whiskers at 1 mm intervals (and stable isotope analysis of these sections), were then correlated to specific giraffe meat feeding bouts and hence growth periods. Knowledge of the duration between giraffe meat feeding bouts enabled the calculation of whisker growth rate and determination of growth pattern. δ13C and δ15N whisker-diet TDFs were estimated for five lions whose diet remained consistent over multiple years. Whiskers removed from four lions at the beginning of the whisker growth experiment, a whisker removed from a female lion as part of a pilot study a year before the experiment and the diet (chicken and beef) samples collected during the experiment were analysed for their isotopic ratios. These were used to calculate isotopic differences between lion whiskers and diet.

Cellulose whiskers (CWs) obtained from naturally occuring cellulose are nano-inclusions which show a lot of promise as mechanical reinforcements in polymers. Typically, a relatively high content is added to realize improvement in effective mechanical behavior. This enhancement in modulus is usually followed by a modest increase in strength but generally the ductility and toughness decrease. Our approach is to use small concentrations of CWs so as not to detrimentally affect processability, toughness and ductility. By aligning the small concentrations, we target the same kind of improvement in modulus and strength as reported in the literature, but at much smaller volume contents. In this work, we investigate the effect of AC electric field on the alignment of dispersed nanoscale CW in a polymer. Polyvinyl acetate (PVAc) is used as the model polymer because of the good interaction between CWs and PVAc. A low concentration of 0.4wt% was used for the study. Two dispersion methods, namely basic and modified, were developed. The basic method led to micron scale dispersion. Using the modified method, CWs were individually dispersed in PVAc with average lengths and diameters of 260 nm and 8 nm respectively yielding an aspect ratio of approximately 30. The behavior of CWs (alignment and chain formation) under an applied electric field was found to be a function of applied electric field magnitude, frequency and duration. Following alignment, the CW/PVAc nanocomposites are thermally dried in the presence of electric field to maintain the aligned microstructure. Improvements in dielectric constant and mechanical properties were observed for the aligned cases as compared to random case and pure PVAc. The optimal electric field magnitude, frequency and duration for the alignment and chain formation were found to be 200Vpp/mm, 50 KHz for duration of 20 minutes for the microcomposite and 250Vpp/mm, 10KHz for a duration of 1hr for the nanocomposite. At 0.4wt% concentration, 21% increase in dielectric constant for the optimal nanocomposite case. Above Tg, a 680% improvement in elastic modulus at 0.4wt% concentration for the optimal nanocomposite case. The reason for the significant reinforcement is attributed to alignment (rotation and chain formation) and chain-chain interaction (3D network formation and hydrogen bonding).

The vibrissal system of pinnipeds relies on sturdy, specialized vibrissae and supporting neural architecture apparently designed for the reception of waterborne disturbances. Although it is known that pinnipeds can use their vibrissae for fine-scale tactile discrimination and hydrodynamic detection, many aspects of vibrissal function remain poorly understood. The present work examined the adaptive significance of vibrissal structure, the sensitivity of the vibrissal system, and the signals received by this system. All of these points were considered with respect to their function in hydrodynamic reception. Four methods of study: laser vibrometry, computed tomography (CT) scanning, psychophysical testing and animal-borne tagging were used to investigate the functioning of this sensory system. Laser vibrometer recordings were used to investigate the effect of vibrissal surface structure and orientation on flow-induced vibrations in excised vibrissae. Vibrations were recorded from the shaft of excised vibrissae exposed to laminar water flow in a flume tank. Samples from three pinniped species were tested: the harbor seal (Phoca vitulina), northern elephant seal (Mirounga angustirostris) and California sea lion (Zalophus californianus). The vibrissae of the seals had an undulated surface structure, while the vibrissae of the sea lion had a smooth surface. No significant difference between species, and therefore surface structure, was observed. However, when vibrissae were tested at three angles of orientation to the water flow, a strong effect of orientation on vibration frequency and velocity was observed across species. CT scanning data revealed that the vibrissae of all the species tested had flattened cross-sectional profiles. This cross-sectional flattening could account for the observed orientation effects. Furthermore, this morphological characteristic may represent an adaptation for improved functioning in the aquatic environment by reducing self-induced-noise from swimming and potentially enhancing detection of signals from other planes. Psychophysical testing was conducted with a trained harbor seal in order to investigate the sensitivity of the vibrissal system of this species. A behavioral procedure was used to measure absolute detection thresholds for sinusoidal stimuli delivered to the vibrissae by a vibrating plate. Thresholds were measured at 9 discrete frequencies from 10 to 1000 Hz. The seal's performance in this stimulus detection task showed that the vibrissal array was sensitive to directly coupled vibrations across the range of frequencies tested, with best sensitivity of 0.09 mm/s at 80 Hz. The velocity thresholds as a function of frequency showed a characteristic U-shaped curve with a gradual low-frequency roll-off below 80 Hz and a steeper high-frequency roll-off above 250 Hz. The thresholds measured for the harbor seal in this study were about 100 times more sensitive than previous in-air measures of vibrissal sensitivity for this species. The results were similar to those reported by others for the detection of waterborne vibrations, but show an extended range of frequency sensitivity. Animal-borne tagging methods were used to investigate the signals received by the vibrissae and better understand the relevant signal components involved in hydrodynamic detection. A novel tagging system, wLogger, was developed to record vibrations directly from a vibrissa by means of an accelerometer coupled to the vibrissal shaft. Laboratory testing using excised whiskers in a water flume confirmed that the tag is capable of recording vibrational signals without hampering the natural movement of the vibrissa. In addition, the tag successfully measured vibrations from the vibrissae of a harbor seal during active swimming and hydrodynamic detection. Live animal testing, along with the supplemental recordings from excised vibrissae, revealed that interaction with hydrodynamic disturbances disrupted the vibrational signal received by the whisker. When exposed to a hydrodynamic signal, whisker vibrations increased in bandwidth, spreading energy across a wider range of frequencies. This finding suggests that modulation of the vibrational signal may play a key role in the detection of hydrodynamic stimuli by the seal. The results of this dissertation research provide insight into the functioning of the vibrissal system in pinnipeds and establishes the groundwork for future pathways of investigation. By investigating the vibrissal system from the focal points of structure, sensitivity and received signals, a more comprehensive understanding of this refined sensory modality is emerging.

Thesis (M.S.)--University of Missouri-Columbia, 2008. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on August 13, 2009) Includes bibliographical references.